Experimental Study of Hierarchical Software Defined Radio Controlled Wireless Sensor Network Wasiu Opeyemi Oduola, Nnaemeka Okafor, Oluwaseyi Omotere, Lijun Qian Electrical and Computer Engineering Department Prairie View A&M University Member of Texas A & M University System Prairie View, TX 77446, USA Email: {woduola,onnaemeka,oomotere, liqian}@pvamu.edu Deepak Kataria Consulting Director IP Junction Inc. Bridgewater, NJ 08807, USA Email: Deepak.Kataria@ip-junction.com Abstract—In this paper, we examine an hierarchical Software- Defined Radio (SDR) controlled Wireless Sensor Network (WSN) testbed built in our Wireless Communications Lab. In this testbed, an hierarchical cluster-based topology is employed to fulfill the needs of energy efficiency and scalability where a group of XBOW MicaZ Sensors/Motes in communication with a Universal Software Radio Peripheral (USRP2) forms a cluster. The USRP2s act as cluster heads to perform data collection using the least interfered channels due to their capability in channel sensing and waveform selection. The USRP2 also serves to extend the transmission range of the sensors and eliminates the excessive overhead required in ad hoc WSN cluster heads. The cluster heads receive the data transmission from the motes on multiple channels and relay the data to the central control on a separate channel. It is expected that this testbed would help the research community in understanding and gathering insightful knowledge about SDR controlled WSNs in a practical context. Index Terms— Hierarchical Wireless Sensor Network, Software Defined Radio, USRP. I. I NTRODUCTION In recent years, Wireless Sensor Networks (WSNs) have become ubiquitous due to their wide array of tracking and monitoring applications in several fields of human endeavors such as healthcare, industrial, agricultural, military applica- tions and so on. Further examples are provided in Fig.1. Such WSNs consist of several resource constrained sensor units deployed in a large geographical area for application specific purposes [1], [2]. For instance, in mission-critical applications such as disaster relief and military operation, each organization may deploy its own sensor network and there may be needs for collaboration among the sensor nodes from one organization to another [3]. Thus, it is often desired that the WSN be self-organizing, energy efficient, cost effective and secured with very small sensor node sizes and a sufficiently good performance for the targeted applications. For this large deployment of sensor nodes, the hierarchical structure has been proposed in the literatures [4]–[8] in order to tackle the associated energy efficiency, routing and scalability challenges. The body of knowledge abounds with numerous theoretical studies and simulation results, a better way to complement and bolster confidence in such results is with experimentations and testbed designs and implementation. Recently, researchers are building various WSN testbeds to help the research community Fig. 1. Some application areas of WSN. in understanding and gathering insightful knowledge about WSNs in a more realistic and practical context [1], [9]. This motivates us to contribute to the body of knowledge by building an hierarchical Software-Defined Radio (SDR) controlled WSN using Universal Software Radio Peripheral (USRP2)/GNU Radio open source software and XBOW Mi- caZ Sensors/Motes. This testbed is built and tested in the Wireless Communication Laboratory (WiComLab) of Prairie View A & M University. Software-Defined Radio is an extensively researched tech- nology that has completely transformed the interoperability of radio frequency (RF) communications between hardware radios (such as USRP Front ends) operating on different standards. Our experimental testbed is implemented based on a modified UCLA Zigbees PHY GNUradio applications [10], [11], GNU Radio open source software [12], XBOW MicaZ sensor nodes [13] and USRP2 [14]. The USRP2 is a commer- cial off-the-shelf SDR, which serves as backend gateways or cluster heads for sensor networks. They fit this role because they do not face the stringent resource constraints of in- network nodes. The USRP2/GNU Radio syndicates interoper- ate with the application specific Integrated Circuits, CC2420 on the XBOW MicaZ motes and has an additional range extension function for the motes. An IEEE 802.15.4 monitor 2015 36th IEEE Sarnoff Symposium 978-1-4673-8042-3/15/$31.00 ©2015 IEEE 18